A conventional motor has been disclosed, for example, in Japanese Patent Laid-Open No. Hei 10-108404. This motor is structured so that a bearing holder is attached to a motor base plate, bearings are disposed on both ends of a through hole of the bearing holder, and a shaft of a rotor is supported by the bearings. However, a certain space is required to set between an exposed electric wire such as a coil and a metal member around the exposed electric wire through the legal regulations for electrical safety. Therefore, when a countermeasure is adopted for the legal regulations, a practical motor is, for example, structured as shown in FIG. 6. In this motor, a stator 40 is structured so that a stator core 41 is covered with insulator bobbins 42 and 43 from upper and lower sides in an axial direction for preventing the stator core 41 from contacting with the coil 44, and the coil 44 is wound around the insulator bobbins 42 and 43.
The bearing holder 45 is structured, from an attached side to a motor base plate 46, of a base part 47, a stator press-fitting part 48 and a small diameter part 49 formed at its tip end side. The base part 47 is provided with a larger diameter than the stator press-fitting part 48 and thus a stepped part 50 is formed between the base part 47 and the stator press-fitting part 48, and a stepped part 51 is formed between the stator press-fitting part 48 and a small diameter part 49. The stator core 41 is press-fitted to the stator press-fitting part 48 of the bearing holder 45 and the stator 40 is positioned with respect to the bearing holder 45 by means of that an end face of the stator core 41 is abutted with the stepped part 50. Certain spaces are respectively provided between the upper and lower insulator bobbins 42 and 43 and the bearing holder 45.
The bearing holder 45 is provided with a through hole 63 through which a shaft 56 of a rotor 55 is passed. The bearing holder 45 is provided with a mounting recessed part 52 in the small diameter part 49, which is a tip end part of the bearing holder 45, and an end part of the base part 47 is provided with a mounting recessed part 53. Bearings 65 and 64 are attached to the mounting recessed parts 52 and 53 to rotatably support the shaft 56. The rotor 55 includes a metal rotor case 57 with the shaft 56 as an axial center. The rotor case 57 is provided with a disk part 58 and a tube-like wall part 59 which is extended parallel to the shaft 56 from an outer circumferential edge of the disk part 58. A magnet 60 is fixed to an inner face of the tube-like wall part 59. An inner peripheral face of the magnet 60 is disposed to face an outer peripheral face of the stator 40 through a certain clearance.
A certain space “S” is set between the coil 44 and the motor base plate 46 on the basis of the legal regulations. Similarly, a certain space is required between the coil 44 and the disk part 58 of the rotor case 57 through the legal regulations. In order to surely prevent an electric wire of the coil 44 from contacting with the rotor case 57, an insulation plate 62 is attached to an end face of the insulator bobbin 42 on the upper side in the axial direction to be disposed between the coil 44 and the disk part 58 of the rotor case 57.
However, in FIG. 6, the coil 44 which is wound around the insulator bobbins 42 and 43 is exposed on an outer side and thus larger separated spaces “S” from the metal rotor case 57 and from a circuit wiring and the like on the motor base plate 46 are required through the legal regulation. In addition, the insulation plate 62 is provided between the stator 40 and the disk part 58 of the rotor case 57 and thus it is difficult that the spaces “S” between the stator 40 and the disk part 58 of the rotor case 57 and between the stator 40 and the motor base plate 46 are reduced.
Further, local potting with the use of epoxy material may be applied to a circuit wiring and the like on the motor base plate 46 to secure insulation security. However, its cure time is longer and its linear expansion coefficient under temperature environment is larger and thus it is weak against heat and cold impact and the epoxy local potting is not practical.
In addition, in order to connect the stator 40 with the bearing holder 45, the stator 40 is press-fitted to the bearing holder 45. Therefore, especially when the bearing holder 45 is made of brass or aluminum material, the stepped part 51 or an outer peripheral face of the stator press-fitting part 48 may be shaved by a hole edge of the stator core 41, which is made of iron series, at the time of press-fitting, and in this case, when shavings are remained on the stepped part 50, the stator core 41 cannot be abutted with the stepped part 50. Therefore, accurate positioning of the stator 40 to the bearing holder 45 is not attained. Further, when the shavings are dropped on the motor base plate 46, an electric short circuit may be formed.
Further, in the stator structure where the coil 44 is wound around the insulator bobbins 42 and 43 which are fitted to the stator core 41 from the upper and lower sides, when individual component precisions and accumulation of combined errors are taken into consideration, or when an attitude variation of the stator 40 due to the shaving of the stator press-fitting part 48 or remaining of the shavings is taken into consideration, a clearance between the stator core 41 and the magnet 60 of the rotor 55 cannot be set narrower and thus a size in a radial direction of the motor is not reduced. As a result, the conventional motor is difficult to reduce its size.